I. Field of the Invention
The present invention relates to the field of magnetic tape units which selectively moves magnetic tape and are utilized to both write and read digital data. Such tape units are of two general types. In the first type, the tape moves between a replaceable file reel and a machine reel. In the second type, only one reel is utilized, the tape leaving the reel, passing through a tape processing station, and returning to the reel as an endless loop. The present invention relates to this second type of tape unit.
II. Prior Art
The single-spool type tape unit or single-reel type tape unit within a cartridge is well known in the prior art. Although these tape units have taken a variety of configuration, the basic configuration comprises an endless length of magnetic tape. The combination of tape and hub is called a single-reel or a single-spool tape unit.
Although the prior art single-spool tape units are appropriate for their intended purpose, these units have several drawbacks. One of these drawbacks is that the prior art single-spool tape unit must pass through a complicated tortuous path before returning to the tape reel and before information can be processed at a processing station. The tape must be fed from the inside surface and returned to the outside surface of the tape reel. The tape cannot be reversed or rewound. Normally one must run through the entire reel in order to return to the beginning of the tape.
Probably, the most significant drawback with the prior art single-reel tape units is that these units cannot be operated in rapid access mode to obtain desired information which is located at a given address on the reel in a minimum amount of time. This means that with the prior art devices that the entire reel must be processed serially to the location of the desired information. As such, if the desired information is located midway on the reel, the prior art unit cannot rapidly locate the desired information.
The net result of the above drawbacks is that the access time of the prior art tape unit is relatively long. As is well known to those skilled in the art, the emphasis in data processing technology is to design tape units having relatively short access time. As such the prior art tape units are not suitable for use in an environment where rapid accessing is required.